Version: 2017.2
public static GUILayoutOption ExpandWidth (bool expand);

설명

Option passed to a control to allow or disallow horizontal expansion.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour { void OnGUI() { GUILayout.BeginVertical(); GUILayout.Button("Short Button", GUILayout.ExpandWidth(false)); GUILayout.Button("Very very long Button"); GUILayout.EndVertical(); } }